dplyr - is there a R code for group_by and combinations

Question

Am kindly looking for R code that can calculate the combinations with 2, of the total in each group.

library(dplyr)
    id<-c(1,1,1,1,2,2,2,2,3,3,3,3)
    sex<-c(1,1,1,1,1,1,1,1,1,1,1,1)
    ds<-data.frame(id,sex)
    out1<-ds %>% group_by(id) %>% summarise(n=n())
    

My output should be

 id<-c(1,2,3)
    n<-c(4,4,4)
    ncomb2<-c(6,6,6)
    

Thankyou

Answer 1

I am not sure if the code below is what you are after

out1 <- ds %>%
    group_by(id) %>%
    summarise(n = n()) %>%
    mutate(ncomb2 = choose(n,2))

such that

> out1
# A tibble: 3 x 3
     id     n ncomb2
  <dbl> <int>  <dbl>
1     1     4      6
2     2     4      6
3     3     4      6